Note: Descriptions are shown in the official language in which they were submitted.
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TITLE "S~SPENSION FOR ELECTRO-ACOUSTICAL TRANSDUCERS"
Technical Field
This inven~ion concerns mounting systems for
electro-acoustical transducers. It is particularly
5 applicable to the mounting of small transducers in
small electro-acoustical appliances, such as portable
tape recorders and dictaphones, hand-held portable
tranceivers and hearing aids (including "behind the
ear" and "in the ear" hearing aids). However, the
10 invention is not limited to such applications alone~
For example, it can be used with advantage in
head-mounted transceivers of the type commonly used by
aircraft pilots.
Background Art
In general terms, microphones are devices which
convert, or transduce, acoustical energy into
electrical energy. It is well known that microphones
which use a moving diaphragm are sensitive to vibration
caused by shocks or movement, and that when microphones
20 are subjected to forces causing vibration, they produce
an unwanted signal. The sensitivity to vibration is a
function of design, and thus varies according to the
type of microphone.
Receivers (sometimes called "speakers" or
25 alternatively "earphones", according to the context in
which the term is used) are devices which transduce
electrical energy into acoustical energy. Their
construction includes a motor and diaphragm system
which is driven by an electrical input signal~ When in
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operation, the motor ancl diaphragm system produce
out-of-balance forces in the form of
structure-transmitted vibration.
Appliances such as hearing aids (which use a
5 microphone and receiver simultaneously), small tape
recorders (which contain microphones and sometimes
receivers) and hand-held transceivers (which
alternately use a microphone and a receiver) require
their transducers to be protected against unwanted
10 structure-borne forces.
It is known that the sensitivity of these
transducers (microphones and receivers) to the
reception or transmission of vibration or shock energy
is always a maximum when the forces which cause the
15 unwanted movement are applied in a direction normal to
the plane of the diaphragm of the transducer. The
function of a transducer mounting, therefore, is to
locate the transducer within a defined space and to
isolate it as much as possible from the reception or
20 transmission of unwanted structure-borne vibrational
forces.
The usual transducer mounting system used in
hearing aids and other small electro-acoustical
appliances comprises a short length of hollow resilient
25 tubing (which transmits acoustical energy to the
transducer in the case of a microphone or from the
transducer in the case of a receiver) together with at
least one buffer which is remote from the acoustic
input or output of the transducer. The buffer or
30 buffers act in compression. The effectiveness of the
vibrational isolating properties of this design of
suspension depends largely on the compliance and
damping properties of the material that is used to
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manufacture the tubing and the buffers. A high
compliance is always sought so that the resonance
frequency of the suspension system is both low and away
from the operating frequency range of the appliance. A
5 high degree of damping is also sought to minimise
direct transmission of energy through the suspension
points. These material characteristics are difficult to
obtain in practice and always place stringent
constraints on manufacturing procedures. Despite this
10 knowledge of the required characteristics of suspension
systems, these systems remain a compromise solution in
practice.
Disclosure of the present invention
It is an object of the present invention to
15 provide a new form of suspension or mounting system for
small electro-acoustical transducers which is simple to
put into practice, is economical to produce, and is
more effective than the suspensions which are currently
available because it achieves a higher compliance and
20 therefore has a lower resonance frequency than existing
systems.
This objective is achieved by providing a
moulding of soft rubber or similar material which has
two ends and which is formed to be a close,
25 substantially encapsulating, fit over the transducer.
This moulding is designed to deform largely in shear.
One of the ends of the moulding is tubular and is
adapted to extend from the inlet or outlet port of the
transducer to the acoustical inlet or outlet of the
30 appliance in which the transducer is mounted, and to be
supported by the appliance acoustical inlet or outlet
port or a tube extending therefrom. The other end of
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the moulding (which is also tubular but may be
perforated and could be of a web construction) is
provided with an annular flange so that it may be
mounted, in a manner similar to that in which a grommet
5 is mounted, on a supporting plate or the like having an
aperture therein.
When using this moulding, a transducer is
suspended between two fixed points by a relatively thin
elastomer material. Wires that have to be connected to
10 the transducer can conveniently be passed through the
end of the moulding which is provided with a flange, to
simplify the construction of the appliance.
Thus, according to one form of the present
invention, there is provided a mounting suspension for
15 an electro-acoustical transducer to be supported in a
predetermined location relative to an acoustic input or
output of an appliance, said suspension comprising a
moulding of soft rubber or similar elastomeric
material, said moulding being characterised in that it
20 comprises
a) a transducer-supporting region having a shape
which corresponds to the external shape of the
transducer, said transducer supporting region
being adapted to be a tight fit around the
transducer;
b) a tubular inlet region, extending from said
transducer-supporting region, the end portion of
the tubular inlet region which is remote from
the transducer-supporting region being adapted
to be a close fit over, and to be supported by,
the end region of a tube extending from the
acoustic input or output of the
appliance, said tubular inlet region being
adapted to extend from the
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acoustical inlet or outlet of the transducer to ~ ¦
said input or output of the appliance when the
transducer is located within the 3
transducer-supporting region and the suspension
is incorporated into the appliance; and
c) a tubular foot, extending from the end of
transducer-supporting region which is remote
from said tubular inlet region, said tubular
foot including an annular flange extending
radially from the axis of the tubular foot, said
flange being adapted to retain the tubular foot
in a position in which the tubular foot extends
through an aperture formed in a mounting plate
of the 3ppli ance.
An embodiment of the present invention, in its
(non-limiting) application to hearing aids, will now be
described, with reference to the accompanying drawings.
Brief description of the drawings
Figure 1 illustrates a conventional mounting
20 arrangement for the transducers of a "behind the ear"
type of hearing aid.
Figure 2 is the view AA of Figure 1, partly in
section.
Figure 3 depicts the hearing aid of Figure 1,
25 but with the present invention supporting the
transducers.
Figure 4 is the view BB of Figure 3, partly in
section.
Figure 5 is a sectional view of the present0 invention, as used in the hearing aid of Figure 3.
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Detailed description of illustrated embodiments
The hearing aid of Figure 1 has an acoustical
inlet port 10 and an acoustical outlet port 11. The
outlet port 11 is normally connected by acoustical
5 conducting tubing (not shown) to the ear of a user of
the hearing aid. The inlet port 10 and outlet port 11
each terminate, within the housing of the hearing aid,
in rigid tubes 12 and 13, respectively. The tubes 12
and 13 are connected, by short lengths of rubber tubing
10 14 and 15, respectively, to the microphone 16 and
receiver 17. The short lengths of tubing 14 and 15 are
each a tight fit over respective tubular projections
16A and 17A from the housings of the microphone 16 and
the receiver 17. Projections 16A and 17A are acoustic
15 conduits to, respectively, the input cavity of the
microphone diaphragm and the output cavity of the
receiver.
The diaphragm of the microphone 16 lies
perpendicular to the plane of the paper on which Figure
20 1 is drawn. The diaphragm of the receiver 17 lies in a
plane perpendicular to the plane of the drawing. Both
diaphragms are parallel to the axis of tube 13, tubing
15 and tubular projection 17A.
The microphone 16 and the receiver 17 are
25 mounted on respective supports by buffers which
comprise rubber buckets 18 and 19, respectively. The
buckets 18 and 19 are provided with a plurality of
radially extending rubber spikes 18A and l9A,
respectively, which serve to locate the buckets firmly
30 within their respective supports 20 and 21. Projections
18B and l9B, from the bases of rubber buckets 18 and
19, may not always bear against the supports 20 and 21,
but when they do, they transmit vibrational energy via
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the compression mode. The support 21 is a shaped wall
that may be made of a plastics or a metal material.
Support 20 is normally made from a rigid plastics
material. The wires 22 and 23 from the microphone 16
5 and receiver 17 have to leave the top of the buckets 18
and 19, respectively, and be fed via suitable channels
to the amplification and other circuitry of the hearing
aid (not shown). If, as is the case of the wires 23
from receiver 17 of Figures 1 and 2, those wires have
10 to pass through an aperture in a transducer support,
then an acoustic seal 24 is required at the aperture in
the support.
It will be apparent, therefore, that both the
microphone 16 and the receiver 17 are mounted within
15 the hearing aid housing by a respective two-componen~
suspension comprising a rubber tube (14, 15), and a
rubber bucket with spikes.
With the present invention, as shown in Figures
3, 4 and 5, the transducers of the hearing aid are
20 mounted with a single, moulded suspension 50 of soft
rubber or similar resilient material. The suspension 50
has three major features. As shown in Figure 5, the
three major features are a transducer-supporting region
51 (which is adapted to be a close fit around, and
25 almost encapsulate, a transducer), an inlet tubular
region 52 and a tubular foot 53.
As will be seen from Figures 3 and 4 (where the
components of the hearing aid have been given the same
reference numerals as they have in Figures 1 and 2),
30 the inlet tubular region 52 performs the same function
as the tubes 14 and 15 of the arrangement shown in
Figures 1 and 2. The flange 54 of tubular foot 53
passes thrcugh an aperture in the support for the
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transducers (as in the ma~nner of one flange of a
~rommet) and secures the foot 53 relative to its
associated support. Note the absence of the rubber
spikes 18A and l9A from the present invention.
To fit the suspension of the present invention
over a transducer, the transducer is first wired and
the wiring passed through the central aperture in the
tubular foot 54. The transducer is then inserted into
the transducer supporting region 51. The moulding is
10 then positioned around the transducers so that the
tubular inlet 52 fits over the transducer tubular
projection 16A (if the transducer is a microphone) or
17A (if the transduceri~is a receiver).
Those skilled in this art will recognise that
15 the present invention has the following major benefits
over the prior art:-
a) The mode of suspension is predominantly
shear. This minimises the effect of the
forces producing unwanted vibration of the
transducer diaphragm and provides at least
10 dB more isolation. It also provides a
more precise placement of the transducer
within the defined space for the transducer
than the conventional suspension system.
b) The effectiveness of the suspension is less
critical of the compliance and damping
properties of the material used in
manufacture than in the prior art systems,
a consequence of which is that the
suspension of the present invention is
easier to fabricate.
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c) The present invention provides for easy
passage of electrical connections through
the walls which surround the defined space.
In some cases, such as in hearing aids, it
is essential to isolate the transducer from
transmission of air-borne sound. The
suspension of the present invention
provides access for wiring which is
superior to existing designs (where the
walls have to be breached for access
purposes and the wires protected from
damage as they pass through the walls by a
protective sleeving, by a sealing compound
or by both). A further advantage is that
the wiring passageway in most applications
does not have to be sealed as is required
in existing designs to preserve the
acoustical isolation integrity of the
defined space.
It will also be apparent to those skilled in
this art that modifications of the illustrated example
of the present invention may be made without departing
from the present inventive concept. For example, the
illustrated embodiment of the present invention shows
25 the moulding as a continuous member, but in practice
the region 51 may contain perforations or may be formed
in the manner of a web, without affecting the
suspension properties of the moulding.
Furthermore, the flange 54 may have an annular
30 slot formed in it, so that the mounting of the foot of
the suspension 50 on a wall i5 effected with the wall
projecting into the slot and part of the flange
extending over each face of the wal] in the region of
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the vicinity of the mounting aperture in the wall (that
is, the mounting of the suspension is effected in
precisely the way in which a grommet is fitted into an
aperture). This variation of the embodiment featured
5 in Figure 5 permits the suspension 50 to have a longer
tubular foot 53, which is an advantageous feature in
some electro-acoustic appliances.
